Human African trypanosomiasis (HAT) occurs in 36 countries in Sub-Saharan Africa, threatening an estimated 60 million people with debilitating disease. No vaccines are available for prevention of infection by Trypanosoma brucei, which causes trypanosomiasis. Without chemotherapeutic treatment, T. brucei kills infected humans. Currently, there are only four drugs approved for the treatment of HAT. All are quite toxic and cause serious side effects and in some cases death (reviewed by Fairlamb, 2003, Trends Parasitol; 19(11):488-94; and Barrett et al., 2007, Br J Pharmacol; 152(8):1155-71). And drug resistance is of concern (for review, see Docampo and Moreno, 2003, Parasitol Res; 90 Supp 1:S10-3). Consequently, there is a strong need for better chemotherapeutic options for the treatment of trypanosomiasis. In addition, additional new drugs must be developed, in order to prepare for possible emergence of drug resistance in the parasites (de Koning, 2001, Int J Parasitol; 31(5-6):512-22; Ouellette, 2001, Trop Med Int Health; 6(11):874-82; and Sinyangwe et al., 2004, Vet Parasitol; 119(2-3):12-35).
Unique to T. brucei is the expression of a variable surface glycoprotein (VSG) coat on the cell surface, which undergoes constant variation in order to evade the humoral immune system and host antibodies. It is thought that recombination from a repertoire of greater that 1,000 VSG genes is responsible for the vast diversity of the parasite, and its effectiveness in immune evasion. This “antigenic variation” allows T. brucei to survive in the host blood stream by evading immune response. VSGs arrive at the plasma membrane after entering the secretory pathway at the endoplasmic reticulum (ER) (McConville et al., 2002, Microbiol Mol Biol Rev; 66(1):122-54). The transferrin receptor and nucleobase/nucleoside transporters are other proteins that localize to the plasma membrane after signal peptide dependent import into the ER. Thus, movement of proteins into the ER is crucial for targeting of cell surface receptors and nutrient transporters, as well as for the biogenesis of the Golgi complex, lysosomes, endosomes and the inner nuclear membrane. From the perspective of eukaryotic pathogen control, small molecules that selectively interfere with translocation of proteins into the ER hold promise for treatment of disease because they could block delivery of many proteins to the plasma membrane and as a result compromise viability of parasites. There is a need for efficient, cost-effective assays for identifying drug targets that interfere with protein translocation in trypanosomes.